1. Field of the Invention
The field of invention relates to downhole completions equipment and method of use. More specifically, the field relates to the prevention of tubing casing annulus (TCA) communication.
2. Description of the Related Art
After a wellbore is drilled to the required depth to access a hydrocarbon-bearing formation, a well completion assembly is introduced into and installed proximate to the hydrocarbon-bearing formation to allow controlled hydrocarbon production to the surface using production tubing. The completion assembly restricts produced fluid from traveling up the wellbore by funneling the produced fluid into production tubing that runs to the surface.
The completion assembly is constructed in the wellbore after installing a liner hanger packer. The liner hanger packer has slips that engage the casing and elastic elements that provide a pressure seal against the casing. A completion assembly is usually run in two phases. The first part is a lower completion assembly, which often includes the lower section of the production tubing proximate to the reservoir interface and a polished bore receptacle (PBR). The PBR is set uphole of the liner hanger packer. Lower completion may include sand screens or fracturing systems to enhance the flow from the reservoir. After installing the lower completion assembly, the upper completion assembly is introduced into the wellbore, positioned uphole of the PBR, and “stabbed” into the PBR such that the seal stack of the upper completion assembly forms several seals against fluids with the interior of the PBR. The seal stack often has multiple sealing elements for redundancy. The seal stack prevents hydrocarbon production fluid from leaking into the wellbore uphole of the liner hanger packer from the PBR (hydrocarbon fluid bypass). The upper completion assembly also provides connectivity through the production tubular connection between the lower assembly and the surface. The upper completion assembly is operable to move within the PBR while the steal stack maintains frictional contact with the PBR. Changes with temperature of the fluid within the wellbore or the production fluid within the production tubing can cause the production tubing string to either expand or contract, pushing the upper completion assembly downhole or uphole along the interior of the PBR. After finishing installation of the completions assembly, the volume of wellbore located uphole of the liner hanger packer and in-between the tubing fluid conduit and the casing is usually referred to as the tubing casing annulus (TCA).
If during production hydrocarbon fluid bypass occurs and hydrocarbons enter the TCA, the industry refers to this as a “TCA pressure communication” or “TCA communication”. This is usually detectable by a temperature rise in the annular fluid or an increase in the pressure of the annulus if the annular fluid is shut in.
TCA communication is a common problem in the gas production industry. A leak through the seal stack inside the PBR is the usual culprit. The main cause is damage to the seal stack inside the PBR due to movement of the seal stack (installation, “stabbing”, stimulation treatments) in the presence of debris around the seals. Debris lodged between the seals and the PBR can cause damage to both the seals and the smooth bore interior surface (gouging) when the seals. The seal stack seals require a smooth, machined surface to seal and are therefore very sensitive to any debris caught between the PBR and the seals. There are several other reasons it could be caused. Chemical or thermal degradation of the seal stack seals may have occurred. Wellbore and formation treatments can expose the seals to severe chemicals or increased fluid temperatures that cause the seals to degrade, albeit over time, such as through reaction of a minor components within the seal or through leeching of plasticizer that maintains pliability. The elastomer, plastomer or rubber material of the seals may have degraded with time in the high-temperature hydrocarbon-rich environment. The seals are not designed to change shape, form or volume (shrink or swell), and so anything that could cause them to retract or expand, especially repeatedly, can cause the formation of cracks in the seal that eventually leads to a rupture. The relative inflexibility of the design is a strength for forming the frictional seal, but it also results in the seal not being able to be repaired in place once the any defect is manifested, especially if the fluid is abrasive (gas or solids) in nature: the flow through the defect will degrade the polymer/rubber matrix material quickly. Finally, the seals may have been physically degraded with “stinging in” and “stinging out” repeatedly—simple wear and tear.
If TCA communication is detected, the current solution in the oil and gas industry is to perform a “workover” using a workover rig. The workover rig removes the upper completion, sets both a new liner hanger packer and a PBR uphole of the original (ensuring that neither of these pieces of equipment were the culprit of the TCA communication), and then a new upper completion is introduced and stabbed into the new lower completion. Essentially, a second completion is performed on the well. This is a time consuming and therefore costly solution. A TCA workover to repair TCA communication in a natural gas well averages around $5 MM per well. In addition, the prolonged shutdowns of a gas well (referred to “locked in potential”) may create additional costs in deferred profits or even force majeure in severe cases due to deferred production. It is also not a perfect solution: the equipment associated with the old liner hanger packer and PBR may interfere with production potential by providing a downhole restriction.
It is desirable to develop an apparatus and method to prevent TCA communication from occurring to not only mitigate potential TCA communication problems, which improve on-time delivery and production reliability of hydrocarbon products, but also use traditional upper/lower completions assembly equipment such that operators and contractors are familiar with the equipment and the methods of installation. Familiarity should maintain or reduce installation time and should improve both construction and operational safety for operators and contractors.